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Date:	Tue, 10 Nov 2009 12:26:32 +0900
From:	InKi Dae <>
To:	Richard Purdie <>
Cc:,, Kyungmin Park <>,
	Andrew Morton <>,
	Pavel Machek <>
Subject: Re: [patch] added brightness feature to lcd class.

Thank you for your comments.

it is a good idea that lcd driver registers interfaces to lcd class
and backlight class.
but I think for AMOLED LCD Panel, backlight couldn't be real device so
power on/off
for backlight device doesn't make sense.

I had tried lcd driver registers interfaces to lcd class and backlight
class as you said.
and also backlight fake driver as Pavel said.

but I thought to use my patch is more simple and effective.
of course, this patch has a problem that it has different path from
backlight class
for controlling brightness.

how about creating symbolic link file for competiability?

Best Regards,
InKi Dae.

2009/11/10 Richard Purdie <>:
> On Mon, 2009-11-02 at 17:50 +0900, InKi Dae wrote:
>> This patch adds brightness feature to lcd class.
>> (kernel/driver/video/backlight/lcd.c)
>> In the past, most of the lcd panels for embedded system was TFT-LCD
>> Panel needing backlight device.
>> But now AMOLED LCD Panel appeared so we should consider brightness
>> control for AMOLED Panel.
>> For the time being, I used backlight fake driver for brightness
>> control of AMOLED LCD Panel.
>> But this way is not good, so I propose to add brightness feature to lcd class.
>> For this, I attached patch file and if my proposal is approved
>> Then I will send s6e63m0 and tl2796 AMOLED lcd panel driver based on
>> lcd class modified soon.
> Pavel has a good point but let me try and explain it differently.
> The point of the backlight class is to expose a backlight brightness
> control to userspace in a consistent well defined way. Anyone wishing to
> write a piece of software to control the brightness of a backlight then
> only needs to support *one* interface.
> It is entirely accepted and normal that multiple "class" devices may
> appear in userspace for one piece of physical hardware.
> Your patch duplicates a userspace API and means any backlight
> application would have to look for *two* different interfaces. This is
> unacceptable.
> Why can't your driver just register a backlight interface and an LCD
> interface? I'd imagine your backlight and LCD can be powered on/off
> separately too.
> Please also cc: the backlight/lcd maintainer (me) on backlight/lcd
> patches in future.
> Andrew: Can you drop that patch from -mm please as I'm not convinced we
> need two backlight brightness interfaces around...
> Cheers,
> Richard
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